Land #10638, Warn when listing inactive sessions without DB connection

Replaces confusing message and stack trace with a warning message,
when the `sessions -d` command is used to list inactive sessions
when no database is connected.

lib/msf/base/serializer/readable_text.rb

@@ -612,10 +612,12 @@ class ReadableText
           'Indent' => indent,
           'SortIndex' => 1)
 
-      framework.db.sessions.each do |session|
-        unless session.closed_at.nil?
-          row = create_mdm_session_row(session, show_extended)
-          tbl << row
+      if framework.db.active
+        framework.db.sessions.each do |session|
+          unless session.closed_at.nil?
+            row = create_mdm_session_row(session, show_extended)
+            tbl << row
+          end
         end
       end
 

lib/msf/ui/console/command_dispatcher/core.rb

@@ -1205,6 +1205,10 @@ class Core
       end
     end
 
+    if show_inactive && !framework.db.active
+      print_warning("Database not connected; list of inactive sessions unavailable")
+    end
+
     last_known_timeout = nil
 
     # Now, perform the actual method